In conventional wrenches of the above-mentioned type, the movable jaw is moved relative to the fixed jaw by means of a manually rotatable roller mounted on a shaft and having an external helical cam engaging sloping teeth on the movable jaw. Adjustment of such wrenches to different effective mouth widths is a time-consuming and tiresome procedure, especially if the effective size varies considerably and often.
The wrench according to U.S. Pat. No. 1,386,596 has a locking means which serves to lock the jaws in a desired position and which is in the form of a finger manually shiftable between two end positions and cooperating with a separate rack specially designed for this purpose. The gear, on the other hand, engages another rack on the handle. Designing, in this manner, the movable jaw with two racks is possible in the rather odd wrench construction disclosed in this patent specification, but in wrenches of more conventional design and of the type with which the present invention is concerned, this is inconceivable in actual practice. As has been stated below, the invention, however, relies on a solution where the gear in question engages, on the one hand, a rack on the movable jaw and, on the other hand, at the same time normally engages a splined coupling which serves as a locking means. In the present invention, this splined coupling is arranged such that, when no pressure is exerted on a push member, it holds the gear in locking position. This locking engagement can be released by actuation of said push member, more particularly when the wrench is applied to a nut or the like, whereupon the spring causes the splined coupling automatically to return to locking position as soon as the push member is released. In the construction according to U.S. Pat. No. 1,386,596, however, the finger must be moved back into engagement with the rack for locking. The provision of the rocker in the construction according to the present invention makes it possible to locate the push member at a point along the handle readily accessible to the operator's hand.
The wrench according to U.S. Pat. No. 4,454,791 comprises, it is true, a rotatable gear, but the locking device for this gear bears no resemblance whatsoever with the locking device which is used in the present invention. In the wrench according to U.S. Pat. No. 4,454,791, the gear thus is locked by means of a laterally movable locking member by which automatic return into locking position can never be accomplished, as is required in the present invention.